@Carieoates, I just saw your post from earlier when you were in Brisbane. Yes, it is a huge environmental problem over here. Feral cats, i.e. those that have been either dumped by irresponsible people, or those that have run away, do enormous damage to the wildlife here.
Australia has the worst extinction rate of small mammals in the world due to cats, foxes and land clearing. In and around Brisbane koalas are in danger as dogs are let out and attack them. We used to have to keep a close eye on ours otherwise they would have killed goannas, koalas, kangaroos, anything, that instinct never goes away, however much they are fed.
As an environmental professional, it is a big passion of mine and I do everything I can to educate people about the damage pets do, and especially cats as they don't seem to be subject to the same controls as dogs when they should be.
Don't get me wrong, I love cats,and had three in the UK, and dogs, but I also love the wildlife here and in the UK and want to see it protected. I don't buy the argument that cats are creatures of instinct and should be allowed to roam. Here many councils now have curfews against roaming cats as well as dogs to try and stop them killing birds, lizards, small mammals and people are fined if they are picked up.
Ok, off my soapbox now. I'm not having a go at anyone, I love my pets as much as everyone else on here, but I also love wildlife as I'm sure many of you do too. We can have both, just with a bit of careful management.